The present invention relates to an apparatus and method for separating hydrocarbons from fluids in a well. More particularly, the present invention relates to an apparatus and method for controlling such separation by the relative permeability between the hydrocarbons and well fluids.
Hydrocarbons such as oil and gas are produced from subsurface reservoirs. The reservoirs also contain water and other well fluids located in the interstitial pore space in the reservoir formations. In many wells, the water volume substantially exceeds the relative volume of hydrocarbons. Accordingly, the hydrocarbon production rate is limited by the volume of water handled by the well fluid production equipment. As the well fluids are produced, the excess water and hydrocarbons are typically separated at the well surface, and the excess water is discharged or reinjected into subsurface formations.
When a wellbore perforates the reservoir and a perforated tubing is positioned within the wellbore, downhole reservoir pressure flows the hydrocarbons and well fluids toward the tubing interior and to the well surface. If the subsurface well pressures are sufficiently large, the hydrocarbons and well fluids are produced to the well surface. In low pressure wells, or as the subsurface well pressures decline during the producing life of a well, the reservoir pressure does not sustain hydrocarbon production to the well surface. Various techniques, such as rod pumps and electric submersible pumps, artificially lift the well fluids to the well surface.
Although surface separator equipment typically removes excess water from produced hydrocarbons, other separation techniques have been attempted to accomplish such separation downhole in the wellbore. For example, electric powered centrifugal separators have been positioned downhole to generate a fluid separating vortex within the downhole separator. However, such equipment requires power and moving components subject to wear and failure. Additionally, such equipment mechanically agitates the well fluids, thereby modifying the separation characteristics of such fluids.
Accordingly, a need exists for an improved apparatus and method for separating hydrocarbons from well fluids produced from a subsurface reservoir. The apparatus and method should economically provide such separation for otherwise marginal wells, and should be adaptable to the production of high hydrocarbon flow rates.